Selective talking and ringing telephone system



July 30, 1935.

c. AUTH SELECTIVE TALKING AND R INGING TELEPHONE SYSTEM Filed March 10, 1935 um: mw M R ws m ml m r M In Patented July 30, 1935 SELECTIVE TALKING AND RINGING TELEPHONE SYSTEM Charles Auth, New York, N. Y.

Application March 10,

4 Claims.

lhis invention relates to selective talking and ringing telephone systems, more particularly to such systems for use for intercommunication be- In systems heretofore employed, selector switches generally similar to the type herein disclosed were employed. The construction was such that when a party was through making a'call the selector switch had to be returned to neutral or no contact position. If this was not done, the next time this party received a call histelephone would. be connected not only to the telephone calling him, but also to the telephone to which his selector switch was connected. The possibility of having cross-talk in a system of this kind is obvious and for this reason the idea, in connection with the system in which the selector switch had to be returned manually, was finally abancloned. It was succeeded by a telephone having a selector switch provided with a ratchet mechanism which would hold the selector switch in operated position, if the switch was rotated while the receiver was off the hook. Replacing the receiver on the hook caused the automatic release of the ratchet and a return of the selector switch to its no-co'nt'act position. It was found that the mechanical wear and tear of this type prevented this type from being successful.

Locking type buttons have also been used extensively for selective talking systems. In this system, one button is provided for each telephone in the system. Each button has two sets of contact springs, one of which is a ringing contact closed only while the button is fully depressed. and the other of which is a talking contact which is mechanically looked after the callers finger has been removed from the button permitting a partial return to normal. A flexible locking mechanism is provided whereby the depression of any button releases the last button locked in to prevent cross-talk. Two means are generally used for tripping the last button depressed; first, a mechanical attachment on the receiver hook which trips the locking mechanism for the buttons when the receiver is hung up, and, secondly, an additional button called the answer button is pressed to trip the locking mechanism before a connecting call can be answered. Both of the systems above referred to are expensive to manufacture and are troublesome mechanically. I V 7 Among the objects of my invention are the p vision of a system in which all the objectionable features above referred to are eliminated, and in which are included means tor preventing any 1933-, Serial No. 660,232

(Cl. 179-40) v cross-talk even in the case where the selector switch of the receiving telephone is left in the last calling position. 7 7

Another object of the invention consists in the provision of mechanism whereby the selector switch may be left in the last calling position, er may be normally kept in any position corresponding to a telephone which is called more fiequenn 1y than the other telephones of the system, and which is efifectively operable to select said'tele- 16 phone upon operation or a ringing button, the construction being such that any calls received will not be cross-connected with said selected telephone except when desired.

Another object or the mvemion consists in the provision of a selector switch for individually con necting the line wires from other telephones of the system to the receiver, transmitter and hook switch circuit of the calling telephone instrument, the provision of a series contact iiii terposed in the circuit between the selector switch and the receiver, transmitter and hook switch circuit, a push button or switch for controlling ringing current to audible signals or other tele' phones, automatic means cont'rcllin'g said series 5 contact to close it when the ringing button is operated after the receiver has been removed from the hook, and means for locking the series contact. in closed position until the'receiver' is replaced on the hook, which action automatically '0 restores the series contact to the original open position. y i

Other objects of the invention will appear from the following" description taken in connection with the drawing, in which I v Fig. 1 is a diagrammatic view of a systein oi telephones constructed, operated and controlled in accordance with my invention; and

Fig. 2 shows a modification of the wiring die. gram of a telephone instrument and it's confirm- 40 ling means. 7 r

By reference to Fig. 1 it will be noted that I have shown a telephone system including five tel ephones of which, for the purpose of illustration,

I have deemed it sufilcient to show two telephone 45 instruments diagrammatically. It is understood, of course, that the number of telephones in the system may be increased by increasingthe num' ber of contacts on the selector switches. I In these I drawings I have illustrated telephone instruments 50 Nos. 3 and 5, the corresponding parts of which are indicated by similar refre'ncelletters with appended numerals corresponding to the 1mmshown.

'L by assuming that a call is to be made from telecontacts i3 for connection with contact g3 and 9,. retardation coil relayRCR3,'the-other terminal Each telephone instrument, as for example the one at the left of Fig. 1, which is arbitrarily assumed to be instrument No. 5, includes the usual form of transmitter and receiver and hook switch BS5 cooperating with the contacts a5, b5 and 05. When the receiver is on the hook switch, ringing battery is connected through the buzzer B5, contact 05 and hook switch H85, to the home line HL5 for this instrument.

Each telephone instrument is also equipped with a selector switch designated SW5 for telephone instrument 5, which is adapted to be moved on to contacts I, 2, 3 and 4, to which home lines HLI to H114 from the other telephone instruments are connected. The switch SW5 is connected to a contact e5 of a push button RB5 by means of which the switch may be connected to the positive side of ringing battery RB. The selector switch SW5 is also connected to contact g5 with which cooperates the armature 72.5 of a retardation coil relay ROB/5 to connect the selector switch to the coil of said relay and to contact i5 which is connected to contact D5 of the hook switch I-IS5 by means of which the receiver, transmitter and selector switch are placed in series upon operation of therelay RCR5. The ringing button BB5 at its contact d5closes a circuit over the relay RCR5 from the terminals of the talking battery TB.

Theoperation of the system may be explained telephone instrument No. 3 with the home line HL5 of the desired telephone No. 5.

The receiver No. 3 is lifted from the hook switch H83 which bridges the contacts a3 and b3 thereby.

connecting the receiver and transmitter of the No. 3 telephoneinstrument in series to the series across the selector switch SW3 with the home line HL5 of the telephone instrument No. 5. Lifting the receiver from the hook also opens a connection between the home line HL3 and the buzzer B3, thus preventing operation of thecontact 423 of ringing button BB3, and across the selector switch SW3, contact 5 and home line HL5 to the telephone instrument No. 5 called, the current passing throughthe hook switch H85 and contact 05 and buzzer B5 of the called station to the negative side of the ringing battery RB.

- The action of pressing the ringing button BB3 also feeds talking battery over line m and contact d3 of ringing button RB3 to the coil of the ture h3'and contacts g3 and i3.

.i Relay RCR3 is held energized lay positive talking' battery current flowing over the line m, through the receiver and transmitter of both the home and the called station, through the contacts, ar'matureand coil of relay RCR3, re-

turning to negative talking battery, over line 11'. Replacing both receivers on the hooks opens this feed and the relay RC'R3 isautomatically deem-s ergized. The selector switch SW3 'need never be returned to a no-contact position after a call is made. The relay RCR3 only operates on the telephone which does the calling and never on the called telephone. To answer a call from another telephone the user simply lifts his receiver and talks. No other operation is necessary as the position of his selector switch has no efiect because the circuit is open through the series contact.

The automatic means for closing and locking the series contact is so controlled as to be nonoperative unless the receiver is off the hook.

If desired, the automatic means for closing and locking the series contact may be a completely mechanical contrivance, so arranged that a pressing of the ringing button will close the series contact and move it to such a position that it will be locked by an extension of the hook switch when the receiver is oil the hook. Replacing of the receiver on the hook will release this mechanical latch and permit the series contact to return to its normal open position. This mechanical contrivance can be easily arranged so that the pressing of the ringing button, while the receiver is still on the hook, will not result in the series contact locking in the closed position.

- The retardation coil relay RCR is of a conventional design having several contact springs, an armature and several fixed contacts and a single Winding,- as shown. The single winding of the relay servesa double purpose; first, in energizing the relay to actuate the armature to close the-series contact and, second, in serving as a retardation coil or choke to prevent voice currents from passing through the battery instead of through the transmitters and receivers. Retardation coils are necessary in any selective talking telephone system operated from a common battery. 1

In Fig. 2 I have shown a second method of using a relay for operating the series contacts g, h and i. The relay in this case has two independent windings, one winding RC serves as a retardation coil and also forms part of the holding circuitfor the relay; the second winding C is connected to thecontact springs of the ringing button RB and is energized by the full voltage of the ringing battery while the ringing button is being pressed. In all other respects the operation of'the relay is exactly the same as the relays RCR3 and RCR5 in Fig. l.

. A different means of achieving the operation of the relay to automatically close the series contact is to have manual means for moving the relay armature to theenergized position. These manual operating means may be tied in with the operation of a ringing button or may be controlled by an entirely separate operation. In either case, the work accomplished will be the same as that done by the ringing contacts and the extra coil of the relay in Fig. 2, 01' by the single coil of the relay and the extra contacts on the ringing button asin Fig. l.

The system described is based on what is known as the common return type of selective talking system. Such a system utilizes a direct talking wire from each telephone to every other telephone, and; one-talking wire common to all telephones. Another type of system which gives essentially the same service is the full metallic system. In the full metallic system two direct wires are connected to every other telephone in the system. The-only reason for the use of the full .metallic system is that the scheme of wiring permits additional precautions to be taken against cross-talk-interference due to induction of the common battery Wire. The statements made in reference to the system disclosed are applicable to the full metallic system; The changes in the telephone instrument include 'a bi-polar selector switch instead of a single pole and two series contacts instead of one. These contacts may be controlled by'two relays each acting as a relay and retardation coil or by the mechanical means hereinbefore mentioned.

Cross-talk as used in the specification does not refer to the interference which may occur on any telephone system due to leakage of voice currents through wire insulation from one talking wire to another, nor does it refer to such interference between two telephone conversations which may occur onaccount of induction of voice currents from one wire to another adjacent one because the wires are parallel. Crosstalk, caused by either of the above reasons, is a condition arising from the cables connecting the various telephone instruments and where cable runs are short such cross-talk interference is negligible.

Cross-talk in the specification, specifically refers to the interference between conversations which will occur when a direct electrical connection exists between the respective talking wires (wires designated as I-IL) of telephone instruments which are supposed to be independently connected to other telephone instruments for the purpose of private or selective conversation.

The telephone instrument described is designed for operation with like instruments on a telephone system which will permit as many private or selective conversations at one time as there are pairs of telephones on the system. On a system having six such instruments, three independent, private conversations could be carried on simultaneously without interference or crosstalk. The instrument disclosed in the specification is entirely automatic in its prevention of cross-talk between independent conversations and without deliberate intent on the part of the users, such cross-talk cannot occur.

To better illustrate how cross-talk could occur if an automatically operated, series contact such as disclosed were not used, I give below an example based on the assumption that the series contact 9 to i be permanently closed on all the instruments of a telephone system. 'In such a system it would be incumbent on the user to return the selector switch to a no contact position (not shown in Fig. 1) after each conversation is concluded. Failure to do this would result in cross-talk as shown by the following example:

Referring to Fig. I, assume that selector switch SW3 of instrument No. 3 is in a no contact position. Instrument No. 5, wishing to call No. 3, will turn selector switch SW to contact 3 and press ringing button. As soon as receiver No. 3 is removed from the hook a complete talking circuit is in operation using wires I-IL3 and m and using the coil of relay RCR5 as a choke for preventing the modulated voice currents from passing through the relatively low resistance battery (which shunts both telephone instruments) instead of through the receivers. Assume now that at the end of this conversation, the user of instrument No. 5 simply hangs up his receiver and forgets to return his dial to a no contact position. Instrument No. 5 is now called by instrument No. 4 in the regular'manner and instrument No. 3 calls instrument No.- 1. This means that the recelve'r and transmitter of instrument No. 4 will be connected directly to the transmitter and receiver of instrument No. 5 and likewise instrument No. 3 will be connected to instrument No. l, but since the transmitter and receiver of instrument No. 5 are still connected to the transmitter and receiver of instrument No. 3 by virtue of the fact that selector SW5 has not been manually returned to a no contact position, all four telephones are connected together so thatall 'conversations will be common, which condition is referred to in my specification as cross-talk; i

This invention prevents this crosstalk condition by (I) automatically opening the circuit be tween the selector switch andreceiver and transmitter assoon as the receiver is restored to the hook; ('2) by closing the circuit between the selector-switch and receiver and transmitter only when the instrument is used to call another instrument-the series contact on a telephone which receives a call is always open; (3) by having the selector switch so, designed that only one contact may be made at one time; and (4) by utilizing the high impedance of the coil of the RCR relay in the calling telephone to act as a choke to prevent modulated voice currents from passing through the battery and also to prevent the modulated voice currents from other circuits operating from the same battery from getting to the receivers of the operating instruments.

While the invention has been described in detail with respect to certain particular preferred embodiments which give satisfactory results, it will be understood by those skilled in the art, after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended, therefore, in the appended claims to cover all such changes and modifications.

What I claim is:

1. In a telephone instrument for use in a selective talking system, a manually operated selector switch for individually connecting the line wires from other telephones of the system to the receiver, transmitter and hook switch circuit of said telephone instrument, a series contact interposed in the circuit between the selector switch and the receiver, transmitter and hook switch circuit, a push button or switch for controlling ringing current to audible signals of other telephones, automatic means controlling said series contact to close it when the ringing button is operated after the receiver has been removed from the hook, and means for locking said series contact in closed position until the receiver is replaced on the hook which automatically restores the series contact to the original open position.

2. In a telephone instrument for use in a selective talking system, a manually controlled selector switch for individually connecting the line wires from other telephones of the system to the receiver, transmitter and hook switch circuit of said telephone instrument, a series contact interposed in the circuit between the selector switch'and the receiver, transmitter and hook switch circuit, a push button or switch for controlling ringing currents to audible signals of other telephones, a relay controlling said series contact, means for energizing said relay by depression of said push button, and a holding circuit for said relay including said receiver, transmitter and hook switch circuit adapted to be,

closed by said hook switch when the receiver is removed from the hook.

3. In a telephone instrument for use in a selective talking system, a manually controlled selector switch for individually connecting the line wires from other telephones of the system to the receiver, transmitter and hook switchucircuit of said telephone instrument, a series contact interposed in the circuit between the selector switch and the receiver, transmitterand hook switch circuit, a push button or switch for controlling ringing current to audible signals of other telephones, a relay controlling said series contact, means for energizing said relay by depression of said push button, and a holding circuit for said relay including said receiver, transmitter and hook switch circuit adapted to be closed by said hook switch when the receiver is removed from the hook, said relay being provided with two coils, the circuit over one of said coils being closed by said push button for operating said relay and the other of said coils being included in said holding circuit and being adapted to be energized upon operation of said first coil and removing the receiver from said hook switch.

4. In a telephone instrument for use in a selective talking system, a manually operated selector switch for individually connecting the line wires from other telephones of the system to the receiver, transmitter and hook switch circuit of said telephone instrument, a series contact interposed between said selector switch and said receiver, transmitter and hook switch circuit, and a relay for closing said contact and adapted to be held operated over said receiver, transmitter and hook switch circuit, said relay also functioning as a choke coil to prevent cross-talk between the various instruments of the system through the talking battery supply.

CHARLES AUTH. 

